1. Field of the Invention
This invention relates to an image pick-up device, and particularly to improvements in an image pick-up device for picking up the image of an object having different degrees of brightness ranging from a low degree to a high degree.
2. Prior Art
Generally, an image pick-up device using an image pick-up tube or a solid-state image pick-up element is provided with an AGC (automatic gain control) circuit for preventing damage, such as seizure, or for obtaining an image with a suitable degree of brightness. In this connection, it is to be noted that depending upon the type of object being imaged, there may be a mixture of high and low degrees of brightness in the image. For example, when a biological organ is observed with reflected light from a light source, since the surface is wet, the image of the light source itself can be reflected from the surface of the organ, resulting in an image thereof being formed on the image pick-up tube or image pick-up element. In this case, the portion where the image of the light source is formed as a result of the reflected light is very high in brightness, while the other portion desired to be observed is dark. If, in such situation, the AGC circuit is operating, AGC will be applied more to the portion of high brightness, with the portion desired to be observed becoming much darker, thus making it difficult to attain minute observation.
On the other hand, if the AGC circuit is eliminated and instead the sensitivity (applied voltage) of the image pick-up device is increased, there arises a problem that the image pick-up element associated with the portion receiving a greater amount of incident light develops the so-called seizure phenomenon and is thereby damaged.